1. Field of the Invention
The present invention relates to a method of intraoperatively sizing a fracture fixation screw to a desired length, and a measuring and cutting system therefor.
2. Brief Description of the Related Art
When a patient suffers an injury in which a bone is fractured or fragmented, the injury often must be repaired by securing the bone fragments together with fixation elements such as pins and/or screws. The fixation elements may be removed after the bone fragments have fused back together, or alternatively they may be left in place permanently or until they are ultimately absorbed into the patient""s body if the fixation elements are made of a bioabsorbable material.
A surgeon may choose to use either pins or screws or a combination of both to hold the bone fragments together, depending on the size of the fragments and the fixation strength necessary or desired to hold the fragments together. For example, screws provide greater fixation strength and greater pullout strength than pins, but pins may be more useful for securing smaller bone fragments in which the generally wider diameters of screws may risk further damaging the fragments. Where appropriate, however, screws are preferred over pins because of the advantages of greater fixation strength and greater pullout strength as mentioned above.
When fixation screws are to be used, it is typically necessary for the surgeon to have all sizes of the fixation screws on hand at the time of the surgery, unless a particularly experienced surgeon can identify beforehand a more limited size selection (diameter and/or length) of fixation screws to have available for the procedure. This usually requires that the surgeon have available for each surgery a complete set of screws containing screws of every diameter and every length which may be encountered in any fracture fixation procedure. Of course, it is very costly and cumbersome to provide such a large number fixation elements for each procedure, both for the manufacturer to produce the fixation screws in many different lengths and diameters, and for the surgeon or medical facility to purchase and store all of the fixation screws in every available length and diameter.
During the surgery, the surgeon selects the length and diameter of each screw to be installed based upon the size of the bone fragments to be secured together and the depth of the hole drilled for the fixation element. In drilling the hole and selecting the screw, the surgeon generally takes into consideration that the larger the diameter of the fixation screw, the greater the fixation strength provided to the bone. However, if screws having diameters which are too large are used, there is a risk of damaging or further splitting the bone fragments. The length of the screw is selected to accommodate the depth to which the fixation screw is to be inserted, and so that the head of the screw after installation does not sit above the bone surface, as this will interfere with proper healing, among other undesirable effects.
In the event that fixation pins are to be used, it may also be necessary for the surgeon to have pins in a variety of different diameters available in the operating room during surgery. Here, however, several types of pins are known in the prior art in which the length of the pin may be adjusted by the surgeon after insertion into the bone. For example, U.S. Pat. No. 4,869,242 to Galluzzo and U.S. Pat. No. 5,180,388 to DiCarlo each discloses a bone fixation pin in which, after installation into the bone, the protruding portions of the pins are broken off or cut, respectively. The smooth shafts and relatively thin diameters render the fixation pins readily amenable to such revisions after installation.
Other types of fixation devices in which the length may be adjusted intraoperatively are disclosed in U.S. Pat. Nos. 5,997,538 and 6,019,762 to Asnis et al., and Cole, respectively. Asnis discloses a ratcheting bone screw kit which includes a body for penetrating into bone tissue, a screw shaft having a unidirectional stop, a fastening element matingly configured to receive the shaft and which advances in a ratcheting manner along the shaft when rotated relative to the shaft. Similarly, Cole discloses a fixation device comprising a shaft and a head engageable with the shaft and moveable between a first and second position. These devices are each rather complex, Asnis in particular, having several physically distinct and cooperating parts and in which the excess length of one part must also be cut after installation of the device.
Given the superior fixation strength achievable by using fixation screws for bone fracture fixation, it would be desirable if the lengths of fixation screws could be revised instraoperatively without the necessity for a complex arrangement of cooperating parts in the fixation device.
The present invention addresses the needs of the prior art by providing a method and system for intraoperatively revising fixation screws used for bone fracture fixation. Specifically, the invention encompasses a device or devices for intraoperatively measuring and cutting bone fracture fixation screws to desired lengths and for re-sharpening the tip of each cut fixation screw, a method for performing the revision technique, and a method for performing a bone fracture fixation procedure.
The fracture fixation screws are preferably bicortical bioabsorbable screws having a constant diameter shaft and a low profile head. The shaft may be fully threaded or partially threaded and have a tapered/pointed distal tip. Preferably, the screws are provided in a standard length but in a variety of diameters. Washers may be attachable to the head of each fixation screw to provide additional compression, or if any sutures are used in the repair, for securing the sutures around the fixation screw. The washers may have a rounded upper surface and a bottom surface suitable for resting on the bone surface around the hole into which the fixation screw is inserted, or may alternatively have a flat upper surface and a rounded bottom for resting in a counterbore surrounding the hole into which the fixation screw is inserted.
The length of the screws may be adjusted during a fracture fixation operation with the aid of a cutting jig that includes a measuring block which is slidable along a rail adjacent a measuring scale and a holding block to facilitate cutting the distal end of the screw once the desired length has been determined. A tip sharpener may be incorporated into the cutting jig or may be provided separately, for reforming a point at the distal tip of the cut fixation screw.
A preferred method according to the present invention includes selecting an appropriately sized fixation screw to be installed; drilling a hole across the fracture site using an appropriately sized drill bit; forming a countersunk bore across the drilled hole; inserting a measuring tool into the drilled hole to determine the length thereof; tapping either the entire length of the drilled hole or only the distal fragment thereof when the lag technique is to be performed; placing the selected fixation screw into a cutting jig; setting the cutting jig to a measurement corresponding to the measured length of the drilled hole; if the selected fixation screw is longer than the measurement set in the cutting jig; cutting off the excess length from the distal end of the screw; inserting the distal end of the cut fixation screw into the sharpener; turning the screw until a pointed tip has been re-formed at the distal end of the screw; aligning the revised screw with the drilled hole; engaging the revised screw with an appropriately sized driver; and advancing the screw into the drilled hole using the driver until the head of the screw is flush or countersunk with the surface of the bone.
Other features and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings.